the act of shitting in clingfilm stretched over someones open mouth then fucking the mouth and at the point of ejaculation bursting through the clingfilm giving the recipiant a mouthful of shit and spunk

This involves making a small pocket inside your partners mouth (Probably with cling film etc) then fill it with a small amount of poo. Then as you are about to bolt after fucking your partners mouth, thrust really hard and break through the poo-pocket thus filling her mouth with spunk and poo milkshake: Hence a "Hot Lunch" Simple really.

Mac: "Hey Soph, You wanna have a Hot Lunch today?" (He he he)

Soph: Oh yes please, only no sweetcorn this time, it gets stuck in my teeth.

latin: Cacatus manduco
The Hot lunch takes the Hot Carl a steamy step further. One partner uses saran wrap to make a small pocket inside his/her mouth and then fills that pocket with feces (it doesn't matter whose). After the initial set-up, the man proceeds to have sex with the poo pocket, breaking through the saran wrap at the final, climatic second to fill his lover's mouth with a delicious fusion of cum and dump, also known as "cump."
From the book: Dirty Sanchez's Guide to Buck Nasty Sex

The sexual pleasure of the Hot Lunch speaks for itself, but less obvious is the way in which it has helped millions of people overcome their aversions to actual hot lunches by replacing terrifying memories of sweaty school cafeteria food with beautiful, aromatic mouthfuls of cump.